I'd alter O'Dell's script slightly: Don't say "I know it's not a fair thing to ask," because that makes it easy for the other person to say no. And it's not unreasonable to ask people to avoid doing something that gives you a migraine. I'd suggest a lead-in like "This may seem a bit odd" or "I know most people don't have a problem with your perfume, but...." The request is unusual, but not unreasonable, especially if you aren't asking her to avoid all scented products, but only specific things that you have a problem with.
Similarly, I don't wear anything lilac-scented, much as I love lilacs, because my husband's lilac allergy is strong enough that he reacts badly to some lilac-scented lotions and such, as well as to the actual flowers. And when it's lilac season, I make a trip or two to Central Park or the Botanic Garden by myself. "Please don't wear that perfume to work" doesn't mean this woman can't ever use it again.